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[eos/base.git] / util / src / TclTk / tcl8.6.12 / libtommath / bn_mp_rshd.c

diff --git a/util/src/TclTk/tcl8.6.12/libtommath/bn_mp_rshd.c b/util/src/TclTk/tcl8.6.12/libtommath/bn_mp_rshd.c
new file mode 100644 (file)
index 0000000..bb8743e
--- /dev/null
+++ b/util/src/TclTk/tcl8.6.12/libtommath/bn_mp_rshd.c
@@ -0,0 +1,51 @@
+#include "tommath_private.h"
+#ifdef BN_MP_RSHD_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* shift right a certain amount of digits */
+void mp_rshd(mp_int *a, int b)
+{
+   int     x;
+   mp_digit *bottom, *top;
+
+   /* if b <= 0 then ignore it */
+   if (b <= 0) {
+      return;
+   }
+
+   /* if b > used then simply zero it and return */
+   if (a->used <= b) {
+      mp_zero(a);
+      return;
+   }
+
+   /* shift the digits down */
+
+   /* bottom */
+   bottom = a->dp;
+
+   /* top [offset into digits] */
+   top = a->dp + b;
+
+   /* this is implemented as a sliding window where
+    * the window is b-digits long and digits from
+    * the top of the window are copied to the bottom
+    *
+    * e.g.
+
+    b-2 | b-1 | b0 | b1 | b2 | ... | bb |   ---->
+                /\                   |      ---->
+                 \-------------------/      ---->
+    */
+   for (x = 0; x < (a->used - b); x++) {
+      *bottom++ = *top++;
+   }
+
+   /* zero the top digits */
+   MP_ZERO_DIGITS(bottom, a->used - x);
+
+   /* remove excess digits */
+   a->used -= b;
+}
+#endif